1. Field of the Invention
The present invention relates to a spin valve read head stabilized without hard bias layers and, more particularly, to a single antiferromagnetic (AFM) layer that is exchange coupled to the spin valve for stabilizing a free layer and/or pinning a pinned layer of the spin valve.
2. Description of the Related Art
The heart of a computer is an assembly that is referred to as a magnetic disk drive. The magnetic disk drive includes a rotating magnetic disk, write and read heads that are suspended by a suspension arm above the rotating disk and an actuator that swings the suspension arm to place the read and write heads over selected circular tracks on the rotating disk. The read and write heads are directly located on a slider that has an air bearing surface (ABS). The suspension arm biases the slider into contact with the surface of the disk when the disk is not rotating but, when the disk rotates, air is swirled by the rotating disk adjacent the ABS causing the slider to ride on an air bearing a slight distance from the surface of the rotating disk. When the slider rides on the air bearing the write and read heads are employed for writing magnetic impressions to and reading magnetic impressions from the rotating disk. The read and write heads are connected to processing circuitry that operates according to a computer program to implement the writing and reading functions.
The write head includes a coil layer embedded in first, second and third insulation layers (insulation stack), the insulation stack being sandwiched between first and second pole piece layers. A gap is formed between the first and second pole piece layers by a gap layer at an air bearing surface (ABS) of the write head and the pole piece layers are connected at a back gap. Current conducted to the coil layer induces a magnetic field in the pole pieces which causes flux across the gap at the ABS for the purpose of writing the aforementioned magnetic impression in tracks on moving media, such as in circular tracks on the aforementioned rotating disk.
In recent read heads a spin valve sensor is employed for sensing magnetic fields from the rotating magnetic disk. The sensor includes a nonmagnetic conductive layer, hereinafter referred to as a spacer layer, sandwiched between first and second ferromagnetic layers, hereinafter referred to as a pinned layer and a free layer. First and second leads are connected to the spin valve sensor for conducting a sense current therethrough. The magnetization of the pinned layer is pinned perpendicular to the air bearing surface (ABS) and the magnetic moment of the free layer is located parallel to the ABS, but free to rotate in response to external magnetic fields. The magnetization of the pinned layer is typically pinned by exchange coupling with an antiferromagnetic layer.
The thickness of the spacer layer is chosen to be less than the mean free path of conduction electrons through the sensor. With this arrangement, a portion of the conduction electrons is scattered by the interfaces of the spacer layer with each of the pinned and free layers. When the magnetizations of the pinned and free layers are parallel with respect to one another, scattering is minimal and when the magnetizations of the pinned and free layers are antiparallel, scattering is maximized. Changes in scattering alter the resistance of the spin valve sensor in proportion to cos xcex8, where xcex8 is the angle between the magnetizations of the pinned and free layers. In a read mode the resistance of the spin valve sensor changes proportionally to the magnitudes of the magnetic fields from the rotating disk. When a sense current is conducted through the spin valve sensor, resistance changes cause potential changes that are detected and processed as playback signals.
A spin valve sensor is characterized by a magnetoresistive (MR) coefficient that is substantially higher than the MR coefficient of an anisotropic magnetoresistive (AMR) sensor. For this reason a spin valve sensor is sometimes referred to as a giant magnetoresistive (GMR) sensor. When a spin valve sensor employs a single pinned layer it is referred to as a simple spin valve. When the spin valve sensor employs an antiparallel (AP) pinned layer it is referred to as an AP pinned spin valve. A spin valve is also know as a top or bottom spin valve depending upon whether the pinning layer is at the top (formed after the free layer) or at the bottom (before the free layer). A pinning layer in a bottom spin valve is typically made of nickel oxide (NiO). The spin valve sensor is located between first and second nonmagnetic electrically insulative read gap layers and the first and second read gap layers are located between ferromagnetic first and second shield layers. In a merged magnetic head a single ferromagnetic layer functions as the second shield layer of the read head and as the first pole piece layer of the write head. In a piggyback head the second shield layer and the first pole piece layer are separate layers.
It is important that the free layer of the spin valve sensor be magnetically stable. During a typical construction of a spin valve sensor a bilayer photoresist is formed on top of multiple full film layers for the spin valve sensor. These full film layers are then ion milled to form the spin valve sensor with first and second side edges that are typically tapered at an angle xcex8 with respect to a normal to the planes of the layers. First and second hard bias layers and first and second lead layers are then deposited with the bilayer photoresist still in place forming what is known in the art as contiguous junctions of the hard bias and lead layers with the first and second side edges of the spin valve sensor. Magnetostatic fields from the first and second hard bias layers are employed for the purpose of aligning the magnetic moments of the free layer so that they are all in the same direction in a single domain state. Without the hard bias layers the free layer is in a multi-domain state with the magnetic domains being defined by numerous walls. The narrower the track width the greater the magnetic instability of the free layer. When the free layer is subjected to applied magnetic fields from the rotating disk the domain walls move around which creates magnetic noise that is superimposed upon the read signal.
The aforementioned process of making contiguous junctions inherently results in a taper of the first and second side edges of the layers of the sensor. Unfortunately, the greater the angle or taper of the first and second side edges of the spin valve sensor the less the effectiveness of the first and second hard bias layers. When the first and second side edges of the spin valve sensor are tapered the first and second hard bias layers take on the soft magnetic properties of the free layer causing the first and second hard bias layers to be magnetically more soft and less capable of applying a magnetostatic coupling for stabilizing the free layer. The first and second hard bias layers are at their maximum effectiveness when the first and second side edges of the spin valve sensor are vertical or parallel to a normal to the planes of the layers. This vertical configuration has not been obtainable with the bilayer photoresist and ion milling steps for forming the first and second side edges of the spin valve sensor. Accordingly, there is a strong-felt need for a biasing scheme to longitudinally bias the free layer into a single domain state when the first and second side edges of the spin valve sensor are tapered.
Pursuant to the above objective, I investigated a scheme employing first and second antiferromagnetic layers in contact with the first and second side edges of the spin valve sensor for magnetically stabilizing the free layer. A third antiferromagnetic layer was exchange coupled to the pinned layer of the spin valve sensor for pinning the magnetic moment of the pinned layer perpendicular to the ABS. A wafer, upon which multiple read heads were constructed, was subjected to heat in the presence of a magnetic field that was directed longitudinal to the free layer, namely parallel to the ABS along the track width of the read head for setting the magnetic spins of the first and second antiferromagnetic layers in the direction of the applied field. The heat raised the temperature of the entire wafer at or above the blocking temperature of the first and second antiferromagnetic layers. The blocking temperature is the temperature at which the magnetic spins of the first and second antiferromagnetic layers are free to rotate in response to an applied field. The first and second antiferromagnetic layers may be made of a material, such as nickel manganese (NiMn) or platinum manganese (PtMn) which has a high blocking temperature of about 300xc2x0 C. The third antiferromagnetic layer for pinning the pinned layer of the spin valve sensor may be made of a material, such as nickel oxide (NiO) or iridium manganese (IrMn) which has a lower blocking temperature of about 250xc2x0 C.
The wafer was then subjected to heat in the presence of a field which is directed perpendicular to the ABS for setting the magnetic spins of the third antiferromagnetic layer perpendicular to the ABS. Even though the second temperature of 250xc2x0 C. is less than the first temperature of 300xc2x0 C., the setting of the magnetic spins of the third antiferromagnetic layer degraded the initial setting of the magnetic spins of the first and second antiferromagnetic layers. This is due to the fact that even though the second blocking temperature is lower than the first blocking temperature the magnetic spins of the first and second antiferromagnetic layers are partially rotated during the second step of setting the magnetic spins of the third antiferromagnetic layer. This degradation then reduces the effectiveness of the longitudinal biasing of the free layer by the first and second AFM layers. Accordingly, while the scheme of employing antiferromagnetic layers instead of hard biasing layers overcomes the coupling problem, the process steps in setting the third antiferromagnetic layer for pinning the pinned layer degrades the performance of the first and second antiferromagnetic layers which longitudinally bias the free layer.
The present invention provides a single antiferromagnetic layer on the first read gap which is employed for longitudinally biasing the free layer of the spin valve sensor. The single AFM layer has first and second portions located in first and second side regions of the read head and a third portion that is located in a sensor region of the read head. The sensor region of the read head is defined by the width of the bottom of the spin valve sensor and the first and second side regions are located on each side of the sensor region. In a first aspect of the invention the first and second portions of the single antiferromagnetic layer have their magnetic spins oriented longitudinally, namely parallel to the ABS along the track width. These portions are exchange coupled to first and second ferromagnetic layers, which are located in the first and second side regions, and are, in turn, exchange coupled to the first and second side edges of the free layer. Accordingly, the first and second portions of the single AFM layer magnetically stabilize the free layer via the first and second ferromagnetic layers by exchange coupling.
A second aspect of the invention includes the first aspect of the invention and further includes the third portion of the AFM layer, which is located in the sensor region of the read head, having magnetic spins oriented perpendicular to the ABS and exchange coupled to the pinned layer of the spin valve sensor for pinning the magnetic moment of the pinned layer perpendicular to the ABS. Accordingly, the first and second portions of the single AFM layer are employed for magnetically stabilizing the free layer and the third portion of the single AFM layer is employed for pinning the magnetic moment of the pinned layer.
The first aspect of the invention applies to either a top spin valve sensor or a bottom spin valve sensor. The second aspect of the invention applies to a bottom spin valve sensor. A third aspect of the invention applies to a top spin valve sensor. The third aspect of the invention includes the first aspect of the invention and further includes a second AFM layer that is exchange coupled to the pinned layer for pinning a magnetic moment of the pinned layer perpendicular to the ABS.
A method of the invention includes setting the magnetic spins of the third portion of the single AFM layer so that the initial setting of the magnetic spins of the first and second portions of the single AFM layer is not degraded. The first and second portions of the single AFM layer may be set by heat in the presence of a field which is directed longitudinal to the free layer. This may be accomplished at the wafer level or at the row level where the wafer has been cut into rows of heads. Next, a pulse is conducted through the spin valve sensor via first and second terminals on the wafer and the first and second leads causing the free layer to exert a current pulse field on the pinned layer which, in turn, orients the magnetic spins of the third portion of the single AFM layer in the same direction. The pulse heats the head discretely throughout the layers of the spin valve sensor and the third portion of the single AFM layer without unduly heating the first and second portions of the single AFM layer. Accordingly, the third portion of a single AFM layer in the sensor region is set to a perpendicular position without degrading the setting of the longitudinal orientation of the first and second portions of the AFM layer in the passive regions.
The method described hereinabove implements the second aspect of the present invention. A method to implement the first aspect of the invention sets the first and second portions of the single AFM layer. A method to implement the third aspect of the invention includes setting the first and second portions of the AFM layer and further includes setting the second AFM layer in a manner similar to that described for implementing the second aspect of the invention.
An object of the present invention is to provide an effective scheme for longitudinally biasing a free layer of a spin valve sensor without using first and second hard biasing layers.
Another object is to employ an antiferromagnetic scheme for effectively longitudinally biasing a free layer and pin a pinned layer of a spin valve sensor.
A further object is to longitudinally bias the free layer of a spin valve sensor with first and second antiferromagnetic layer portions and pin a pinned layer of the spin valve sensor with a third antiferromagnetic layer portion wherein a setting of the magnetic spins of the third magnetic layer portion does not degrade the setting of the magnetic spins of the first and second antiferromagnetic layer portions.
Still another object is to provide a single antiferromagnetic layer which has first and second portions for longitudinally biasing a free layer and a third portion between the first and second portions for pinning the magnetic moment of a pinned layer of the spin valve sensor perpendicular to the ABS.
Still a further object is to provide a method of making a spin valve read head wherein the setting of the magnetic spins of first and second portions of a single antiferromagnetic layer for longitudinally biasing a free layer is not degraded by magnetically setting the magnetic spins of a third portion of the single antiferromagnetic layer for pinning a magnetic moment of a pinned layer.
Other objects and advantages of the invention will become apparent upon reading the following description taken together with the accompanying drawings.